The invention relates to a method of producing threads and fibers of synthetic materials, in particular materials of high-melting or non-melting polymers, e.g. difficult-to-dissolve or insoluble polymers, such as polytetrafluorethylene.
The known melting-spinning methods or dissolving-spinning methods are not suited for the production of fibers or threads from high-melting or non-melting polymers or from difficult-to-dissolve or insoluble polymers, respectively. Fibers and threads of such polymers are, however, in many cases of great technical interest because of their specific properties. Fibers and threads of polytetrafluorethylene are, for example, remarkable for their high resistivity to temperature and chemicals, as well as for their extremely low adhesion-friction coefficient. Therefore these fibers and threads despite their relatively high costs, are used in the production of special technical articles, such as interwoven sealing packages for stuffing boxes, textures and felts for the filtration of aggressive gases or liquids.
Threads of polytetrafluorethylene are customarily produced in a suspension or matrix-spinning procedure, in which the finest particles of the polymer are suspended in a viscose liquid, e.g. an alkaline solution of sodium-cellulose-xanthate, and are spun together with this liquid. After spinning the cellulose threads are subjected to a thermal treatment in which the matrix disintegrates and the polytetrafluorethylene particles sinter together. Thus stretchable threads are obtained. Originally their color is dark-brown due to carbon residues, but by a special bleaching procedure the threads may be changed into a light-colored product, with a corresponding loss of rigidity.
Austrian Pat. No. 290,710 describes a method of continuously producing fibers and threads of a polymer foil. According to this method a foil is split up into threads by means of cutting tools arranged transverse to the running direction of the foil, while the foil is stretched at the same time. The foils may be produced in a manner known per se, e.g. in the case of polytetrafluorethylene they may be produced by paste extrusion or by peeling cylindrical sintered blocks of polytetrafluorethylene.